The invention relates to a blanking-cap system for a conduit. Although not exclusively, it relates more particularly to a blanking-cap system for an orifice of an air-intake duct into the combustion chamber of a ramjet.
It is known that ramjets consist essentially of a combustion chamber, terminating in an ejection nozzle and into which liquid or gaseous fuel (possibly being obtained from a solid fuel) and combustion air are introduced. This combustion air is introduced into the said combustion chamber through at least one air-intake duct, of the air-scoop type, which traps the air when the said ramjet (or the flying object which carries it) moves with respect to the surrounding air.
Thus, the functioning of a ramjet requires that the said ramjet be speeded up beforehand with respect to the said surrounding air.
To do this, it is usual, in an initial operating phase corresponding to the speeding-up of the said ramjet, to make it operate as a rocket, by virtue of a consumable auxiliary thruster arranged in the said combustion chamber, then, when the said ramjet has reached a predetermined speed and when the said auxiliary thruster has been completely consumed, ramjet operation proper starts, with injection of fuel and of combustion air into the combustion chamber.
Such dual-mode operation (rocket mode, then ramjet mode) demands that a blanking-cap system be provided in order, on the one hand, to blank off an orifice of the said air-intake duct or air scoop during operation as a rocket, in order to prevent leakage, through the said orifice, of the gases generated by the said consumable auxiliary thruster and, on the other hand, to open the said orifice of the air-intake duct or air scoop for operation as a ramjet proper.
It is known to use a swinging hatch, with controlled opening, as blanking-cap system. However, in this case, a particularly sophisticated control system has to be provided, preventing any inadvertent opening of the hatch, which could entail premature firing of the said consumable auxiliary thruster and, consequently, damaging the carrier (aircraft for example) of a missile equipped with the said ramjet. Moreover, above all, this hatch remains present on board the ramjet after the air-intake duct has been opened, which, needless to say, poses problems of bulk and entails the presence of a parasitic mass during ramjet operation.
In order at least partially to remedy this latter drawback, the document FR-2 474 594 describes a blanking-cap system for a combustion-air intake orifice into the combustion chamber of a ramjet, which includes:
a blanking cap or cover made of glass, which completely blanks off the said orifice during the initial phase; and
a destruction device, namely a mechanical percussion device, which destroys this glass blanking cap before ramjet operation. Upon this destruction, the glass blanking cap is broken up into small fragments. As the orifice is located downstream of the air scoop and corresponds to the feed opening into the combustion chamber, these fragments are ejected outwards, rearwards, passing through the combustion chamber and the thrust nozzle.
Consequently, the blanking cap is completely eliminated during ramjet operation.
However, the use of a mechanical percussion device, especially comprising a piston and a striker terminating in a point, exhibits a few drawbacks.
This is because:
either this percussion device acts frontally on the blanking cap, in order to be able to break it easily.
However, in order to obtain such frontal action, it is necessary to arrange the blanking cap in the air-intake duct, such that it then disturbs the airflow in ramjet operation;
or the percussion device is arranged outside the said air-intake duct.
However, in this case, it can only act laterally on the blanking cap, which reduces the effectiveness of this destruction device, since it is much more difficult to break the glass, and above all to break it completely, from such a position.
The object of the present invention is to remedy these drawbacks. It relates to a blanking-cap system for an orifice of a conduit, in particular for an orifice of an air-intake duct into the combustion chamber of a ramjet, which makes it possible:
to open the said orifice of the conduit effectively at a defined instant; and
to free the said conduit completely after the orifice has been opened.
To that end, according to the invention, the said blanking-cap system for a conduit, of the type including:
at least one glass blanking cap capable of completely blanking off the said conduit; and
at least one device for destroying the said glass blanking cap,
is noteworthy in that the said destruction device comprises:
at least one projectile which is capable of destroying the said glass blanking cap when it is projected onto it; and
a controllable projection means, which is capable of projecting the said projectile and which is arranged outside the said conduit while being oriented in such a way as to be able to project the said projectile onto the said blanking cap.
Thus, by virtue of the invention:
as the projection means is arranged outside the conduit, it does not impede the airflow after the opening of the orifice (in ramjet mode, for example), the said conduit being completely freed; and
as the destruction means comprises the projection of a projectile, the glass blanking cap can be destroyed effectively and completely, despite the distance to the projection means and its being arranged outside the said conduit.
Moreover, by virtue of the invention, the projection means can be oriented in such a way that the impact of the projectile on the blanking cap is situated at a spot where complete destruction is facilitated, especially at the most fragile spot on the glass blanking cap, generally in the center thereof, which makes it possible to enhance and to optimize the effectiveness of the destruction.
Consequently, in the particular case of a ramjet, the entire blanking cap is eliminated during ramjet operation, which makes it possible to remedy the drawbacks of bulk and of parasitic mass mentioned above.
In order to optimize the precision of the impact of the projectile on the blanking cap and thus to enhance the effectiveness of the destruction thereof, advantageously, the blanking-cap system in accordance with the invention further includes a straight-line guide for guiding the said projectile, the straight-line guide being produced in the form of a channel, one end of which is situated facing the said projection means and the other end of which is directed towards the said blanking cap.
In the context of the present invention, the projection means, the projectile and the glass of the blanking cap can be produced according to various ordinary embodiments.
However, preferably,:
the said projection means is a pyrotechnic striker;
the said projectile is a bullet (pointed) with a conical, metal head; and
the said blanking cap comprises toughened glass exhibiting a rupture stress of at least 190 Mpa.
It will be noted that the blanking-cap system in accordance with the invention can be employed on various types of conduits, the opening or the unblanking of which must be carried out in the operational environment. This implementation is possible especially by virtue of the abovementioned characteristics of the blanking cap, since it is possible to choose a glass which is capable of withstanding the mechanical, thermal, vibratory and/or electromagnetic stresses likely to be encountered for these various types of conduits.
In one preferred application, the blanking-cap system in accordance with the invention is intended to blank off an orifice of a combustion-air intake duct into the combustion chamber of a ramjet, the said ramjet being capable, in a known way, in an initial phase of operation corresponding to the speeding-up of the said ramjet, of operating as a rocket by virtue of a consumable auxiliary thruster arranged in the said combustion chamber, then, when the said ramjet reaches a predetermined speed, of operating as a ramjet proper with injection of fuel and of combustion air into the said combustion chamber, and the said blanking-cap system including, in a known way:
at least one glass blanking cap capable of completely blanking off the said orifice, during the said initial phase of operation as a rocket; and
at least one destruction device capable of destroying the said glass blanking cap so as to open the said orifice for operation as a ramjet.
According to the invention, the said blanking-cap system is noteworthy in that, in addition to the abovementioned characteristics (relating to the destruction device and the glass blanking cap), the said blanking cap blanks off the inlet orifice into the air-intake duct, upstream thereof in the direction of flow of the air into the said air-intake duct.
Thus, as the projection means is situated within the ramjet, in the region of the air-intake duct (air scoop), but outside it, the projectile ejected by the projection means is, after destruction of the blanking cap, ejected directly out of the ramjet and of the flying machine (missiles, etc.) equipped with this ramjet. Consequently, there is no risk of the said projectile damaging the said ramjet or the said flying machine.
Moreover, since, upon the impact on the blanking cap, the projectile loses a great deal of energy, it is no longer dangerous, after it has been ejected out of the ramjet, for objects (another missile, for example) or persons present in the immediate environment of the said ramjet.
Advantageously, the said blanking cap corresponds to an extension of the outer wall of the ramjet in the region of the said inlet orifice.
Thus, during the initial phase before the change to ramjet operation, as the inlet orifice into the air-intake duct is blanked off and as the blanking cap forms a geometric continuity with the outer wall of the ramjet, the air which slips along this wall also slips along the outer face of the blanking cap, without being disturbed in its flow, which makes it possible particularly to reduce drag.
Advantageously, moreover, the blanking-cap system in accordance with the invention includes at least one fixing means made of elastic material, preferably of rubber, for fixing the said blanking cap onto the said orifice, which makes it possible to damp vibration (due especially to shocks).
Thus, by virtue of this reduction in vibration, it is possible to provide for a lesser thickness of fairing lip (in the region of the said orifice) for fixing the blanking cap.
The invention also relates to a ramjet equipped with a blanking-cap system as mentioned above, as well as a missile comprising such a ramjet.